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Lightspeed Attenuator - Best Preamp Ever?

The question is a bit rhetorical. No preamp is the best ever, and much depends on system context. I am starting this thread beacuase there is a lot of info on this preamp in a Music First Audio Passive...thread, an Slagle AVC Modules...thread and wanted to be sure that information on this amazing product did not get lost in those threads.

I suspect that many folks may give this preamp a try at $450, direct from Australia, so I thought it would be good for current owners and future owners to have a place to describe their experience with this preamp.

It is a passive preamp that uses light LEDs, rather than mechanical contacts, to alter resistance and thereby attenuation of the source signal. It has been extremely hot in the DIY community, since the maker of this preamp provided gernerously provided information on how to make one. The trick is that while there are few parts, getting it done right, the matching of the parts is time consuming and tricky, and to boot, most of use would solder our fingers together if we tried. At $450, don't bother. It is cased in a small chassis that is fully shielded alloy, it gets it's RF sink earth via the interconnects. Vibration doesn't come into it as there is nothing to get vibrated as it's passive, even the active led's are immune as they are gas element, no filaments. The feet I attach are soft silicon/sorbethane compound anyway just in case.

This is not audio jewelry with bling, but solidly made and there is little room (if any) for audionervosa or tweaking.

So is this the best preamp ever? It might be if you have a single source (though you could use a switch box), your source is 2v or higher, your IC from pre-amp to amp is less than 2m to keep capaitance low, your amp is 5kohm input or higher (most any tube amp), and your amp is relatively sensitive (1v input sensitivity or lower v would be just right). In other words, within a passive friendly system (you do have to give this some thought), this is the finest passive preamp I have ever heard, and I have has many ranging form resistor-based to TVCs and AVCs.

In my system, with my equipment, I think it is the best I have heard passive or active, but I lean towards prefering preamp neutrality and transparency, without loosing musicality, dynamics, or the handling of low bass and highs.

If you own one, what are your impressions versus anything you have heard?

Is it the best ever? I suspect for some it may be, and to say that for a $450 product makes it stupidgood.
pubul57
georgehifi's avatar
georgehifi
10,312 posts
 
Banquo363Am I right in believing that non-ideal impedance match between phono stage and LSA results in a attenuation of the high end? Perhaps it hasn't bothered me because of my old ears?Banquo363

No, the slight impedance (resistance)mismatch you have will compress slightly the dynamics, and if ever the output impedance becomes higher than the input impedance then you will attenuate the whole signal, as it then becomes a voltage divider.
What attenuates the highs is lots of cable capacitance.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
If I remember Batalok I think you maybe one of many I may have said the input impedance was a bit low around 30K and suggested that any competent tech could raise it up to 68k or so with 1/2hr work and a 5c resistor.

Cheers George
picky
1 posts
 
I bought a Lightspeed about a year back. It works really well with both the PSAudio DL-III and PWD. It lets a lot of the more subtle details come thru, and with less edginess.
Please note that you need a low-output-impedance source and a high-input-impedance amp to really take advantage of the LS. Both of the PSAudios have 100 ohm outputs, and my amp has 220k ohm inputs with 20dB of gain.
Altogether, given the impedance and gain issues, the LS is certainly worth auditioning. That it costs less than $500 makes it a no-brainer.
batalok
31 posts
 
George, that was done sometime ago but the whole thing became a lot better when the circuit is slightly modified. Let me say imho, the lsa becomes from 3 stars to 4 stars (68k, 1/2 work) to 5 stars (final) in a scale of 5 (1 is worst).
batalok
pubul57 OP
3,712 posts
 
George, in the Warpspeed DIY thread, the poster identified some area we he thought the LSA could be improved:

What I found interesting at the start of the Warpspeed thread was the identification of a few "problems" with the LSA and attempt to improve upon the LSA:

1. the inability to adjust to complete silence
2. on low/high volume level settings, power levels on the LEDs endanger/shorten/toast the life out of the optocouplers
3. the need to improve the power delivery to the optocouplers
4. the need to improve on quality of the volume adjustment pot
5. the Lightspeed, simple as it is, still has a number of variables/design factors that affect performance

What is your view on these issues. On 5, we wonder if perfomance can be improved or you feel that after 30 years of sorting this thing out we are pretty much at the performance limit - obviously some ergonomic issues exists, but might not be addressable without compromising ulitmate performance.
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